Methods and apparatus for completing production wells

ABSTRACT

This application discloses new and improved methods and apparatus for completing production wells having perforations which either are to be cleaned or penetrate earth formations which are to be fractured, acidized, or treated such as, for example, to inhibit the subsequent production of unconsolidated formation materials. To practice the present invention, a new and improved production tool is arranged for coupling into a string of production tubing and includes a typical well packer having an elongated tubular member dependently coupled therebelow and capped at its lower end for defining an enclosed chamber of a substantial volume below the packer which is initially maintained at a reduced pressure by a new and improved normally-closed pressure-actuated valve arranged at the upper end of the tubular member. The production string and the tool are installed in a cased well bore with the packer being set above a previouslyperforated interval traversing an earth formation which is to be subsequently produced. Once the customary wellhead equipment is installed to provide communication from the surface with the tubing, the normally-closed valve is selectively opened by increasing the pressure of the fluids in the production string above the packer. Upon opening of this valve, formation fluids will be suddenly exhausted into the reduced-pressure chamber for removing contaminants that may have previously entered the formation following the perforation of the casing so as to leave only uncontaminated formation materials immediately surrounding the perforations. Thereafter, a selectively-releasable tubing plug in the production tool above the normally-closed valve is removed to permit selected fluids to be pumped by way of the production string through the perforations and into the adjacent earth formations.

United States Patent Young 51 May 16, 1972 [54] METHODS AND APPARATUS FOR COMPLETING PRODUCTION WELLS [72] Inventor:

[73] Assignee:

David E. Young, Houston, Tex.

Schlumberger Technology Corporation, New York, NY.

[22] Filed: June3, 1970 [21] Appl.No.: 43,067

Clark, Jr ..l66/224 Primary Examiner-Joseph l-l. McGlynn Attorney-Ernest R. Archambeau, Jr., David L. Moseley, Edward M. Roney and William R. Sherman 57 ABSTRACT This application discloses new and improved methods and apparatus for completing production wells having perforations which either are to be cleaned or penetrate earth formations which are to be fractured, acidized, or treated such as, for example, to inhibit the subsequent production of unconsolidated formation materials. To practice the present invention, a new and improved production tool is arranged for coupling into a string of production tubing and includes a typical well packer having an elongated tubular member dependently coupled therebelow and capped at its lower end for defining an enclosed chamber of a substantial volume below the packer which is initially maintained at a reduced pressure by a new and improved normally-closed pressure-actuated valve arranged at the upper end of the tubular member. The production string and the tool are installed in a cased well bore with the packer being set above a previously-perforated interval traversing an earth fonnation which is to be subsequently produced. Once the customary wellhead equipment is installed to provide communication from the surface with the tubing, the normally-closed valve is selectively opened by increasing the pressure of the fluids in the production string above the packer. Upon opening of this valve, formation fluids will be suddenly exhausted into the reduced-pressure chamber for removing contaminants that may have previously entered the formation following the perforation of the casing so as to leave only uncontaminated formation materials immediately surrounding the perforations. Thereafter, a selectivelyreleasable tubing plug in the production tool above the normally-closed valve is removed to permit selected fluids to be pumped by way of the production string through the perforations and into the adjacent earth formations.

20 Claims, 5 Drawing Figures PATENTEnMmsm 3,662,834

SHEET 1 BF 2 David E. Young INVENTOR ATTORNEY P A TENTEDMM 1s m:

SHEET 2 BF 2 A TTORNEY METHODS AND APPARATUS FOR COMPLETING PRODUCTION WELLS It is, of course, customary for a cased well bore to be perforated at one or more points to provide fluid communication with selected earth formations therearound. Once the well is perforated, various treating operations such as acidizing, fracturing, or sand-consolidating operations are typically conducted to prepare the well for efficient production. Those skilled in the art will appreciate, however,that it is not at all uncommon for one or more of the perforations along a given perforated interval to be at least partially blocked by loose formation materials, debris, or foreign matter which is usually deposited in a perforation by typical shaped charges. A partial or total blockage of one or more of the perforations will, of course, impede or prohibit the introduction of treating fluids into those perforations and result in the inadequate treatment of at least those portions of the earth formation immediately adjacent thereto. As a result, further and otherwise needless treating operations will ultimately be required. Accordingly, unless all of the perforations along a perforated interval are capable of readily conducting fluids, subsequent treating operations as well as the production rate of the well will be significan'tly impaired.

l-leretofore, such treating operations have had to be conducted before the drillingrig is removed from the well site so that its associated equipment and drill string could be employed. This, of course, results in needless expenses as well as additional delays before the production string and the related surface equipment can be installed to prepare the well for production. I Accordingly, it is an object of the present invention to provide new and improved methods and apparatus for completing wells to obtain improved fluid communication between the well bore and selected earth formations traversed thereby without delaying the installation of the production string and the associated wellhead and surface equipment once the drilling operation is concluded.

This and other objects of the present invention are attained by arranging pressure-actuated valve means in a production string and below a production packer included therewith. The valve means are initially closed to define an enclosed chamber of selected volume in a section of tubing arranged therebelow and capped at its lower end to maintain the chamber at a reduced pressure until after the packer is set and the production string is installed and connectedto the usual wellhead and surface equipment. When the well is to be prepared for production, the valve means are selectively opened from the surface to draw formation fluids into the enclosed chamber for clearing the perforations below the production packer of debris or contaminants that would otherwise impair fluid communication between the production string and the perforated earth formation. Thereafter, barrier means initially arranged in the tubing above the valve means are selectively removed to enable fluids to be pumped from the surface into the well bore below the packer as may be necessary to prepare the well for production.

In the preferred embodiment of the apparatus of the present invention, the valve means are operatively arranged to be selectively opened in response to a predetermined change in the pressure in the production string above a production packer included with the apparatus. In this manner, communication can be selectively established between the perforated interval and the enclosed chamber below the valve means. Selectively-releasable barrier means are operatively arranged in the new and improved tool above the valve means and adapted to be selectively removed therefrom by a releasing tool for establishing communication between the production string and the perforated interval of the well bore below the packer.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of new and improved apparatus and exemplary methods employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIGS. 1, 3 and 4 schematically depict the successive steps of the methods of the present invention;

FIG. 2 shows a typical perforation as it may appear before conducting a completion operation in accordance with the methods of the present invention; and

FIG. 5 depicts a preferred embodiment of the new and improved apparatus of the present invention.

Turning now to FIG. 1, a new and improved production tool 10 arranged in accordance with the principles of the present invention is schematically illustrated as being dependently coupled from the lower end of a string of production tubing 1 1 and positioned in a well bore 12 having acasing 13 secured in place by an external sheath of cement 14. To gain communication with an earth formation 15 traversed by the well bore 12, one or more perforations, as at 16, have been previously produced through the casing 13 and the cement 14 in the usual manner. As is customary, the production tubing is dependently supported in the well bore 12 by a typical wellhead assembly 17 including at least a pair of valves, as at 18 and 19, for selectively controlling communication with the tubing string 11 and the casing 13.

As illustrated in FIG. 1, the tool 10 is comprised of a selectively-settable production packer 20 from which is dependently coupled an elongated tubular body 21 having its lower end capped, as at 22. To provide an enclosed chamber 23 within the tubular body 21 that is initially maintained at a low or atmospheric pressure, normally-closed valve means 24 and selectively-releasable barrier means 25 are arranged on the upper end of the body 21 and adapted to be selectively operated independently of one another. As a matter of convenience, it is, of course, preferred to employ one or more joints of conventional production tubing for the elongated body 21. The chamber 23 can, if desired, be filled with an inert gas that is at selected pressure which is less than the anticipated formation pressure. Although other well packers may, of course, be employed, it is preferred that the packer 20 be one of the production packers shown in either U.S. Pat. No. 3,074,484, or U.S. Pat. No. 3,352,362.

As will be subsequently discussed, the methods of the present invention are uniquely applicable for performing acidizing and fracturing operations as well as sand-consolidation operations after the production string 11 and the wellhead l7 are in position. Accordingly, as depicted in FIG. 2, an enlarged view is shown of one of the perforations 16 as it may well appear after the adjacent formation 15 has been perforated. It will, of course, be appreciated that when a perforating tool (not shown) which typically includes one or more shaped charges is positioned in the well bore 12 and actuated for producing the perforations 16, the perforations will initially extend into the formation 15 as generally represented in FIG. 2.

Irrespective of the nature of the formation, debris (such as at 26) will be left in the formation 15 as a result of the disintegration of a typical shaped charge liner. Moreover, by observing test shots fired into laboratory targets, it is known that a typical shaped charge perforating jet will leave a somewhatimpermeable layer of debris (as indicated at 27) around the walls of the forward portion of the perforation 16. This relatively-impermeable sheath of debris will either remain substantially in the position illustrated at 27; or, if the formation (as at 15) is incompetent, this impermeable layer will most likely be collapsed inwardly as the perforation 16 is filled with loose formation materials. In any event, flow communication between the well bore 12 and the formation 15 will be at least retarded, if not substantially impaired, by the debris 27 and 28 deposited in the perforations 16. It is, therefore, this debris 27 and 28 which, irrespective of the competency of the formation 15, must be removed before the well bore 12 can be successfully completed and production commenced.

Accordingly, as illustrated in FIG. 3, after the packer has been set for isolating the interval of the well bore 12 immediately adjacent to the perforations 16 from the remainder of the well bore thereabove and the wellhead 17 is in position, the valve 24 is opened. It will be appreciated, therefore, that upon opening of the valve 24, a sudden high-pressure differential is developed between the connate fluids in the formation 15 and the enclosed chamber 23 which, preferably, is initially at atmospheric pressure. This sudden pressure differential across the perforated well bore interval will induce a rapid, high-velocity flow of connate fluids, as at 28, from the formation 15 through the various perforations 16 and into the empty chamber 23. These rushing fluids will, therefore, effectively wash out the debris, as at 26 and 27 (FIG. 2), along with any loose formation materials from the perforations 16. As a result, once this sudden flow ceases upon the filling of the chamber 23, the formation 15 surrounding the perforations 16 will be effectively cleaned leaving only clean formation particles adjacent to the perforations.

It is preferred to delay the removal of the barrier means after opening of the valve means 24 so as to allow loose formation particles, debris and the like to settle into the lower portion of the enclosed chamber 23 as well as into the well bore 12 therebelow. Once this is believed to have occurred, the barrier means 25 are removed to establish fluid communication between the wellhead 17 and the formation 15.

The technique employed to remove the barrier means 25 will, of course, be dependent upon the particular apparatus employed therefor. For instance, in one manner of arranging the barrier means 25, a plug, such as that shown generally at 44" in my copending application Ser. No. 43,068 filed simultaneously herewith, can be releasably secured above the valve means 24 and operatively arranged for initially closing the upper end of the chamber 23 until a downwardly-acting mechanical force or unbalanced pressure force is imposed on the plug to drive it downwardly into the enclosed chamber. Alternatively, the barrier means 25 might also be a so-called tubing plug" which is releasably secured in position by a shear pin or typical latching fingers and adapted to be removed by a typical wireline overshot or grapple (not shown) that is lowered through the production string 11 and coupled to an upright fishing neck as at 29. This tubing plug might well be one of those shown on Page 3,788 of the 1968-69 Composite Catalog of Oil Field Equipment and Services.

In any event, once the barrier means 25 have been removed, a fluid, such as at in FIG. 4, is injected into the production string 11 through the wellhead valve 18. Where the formation 15 does not require a treating operation, the fluid 30 needs only to be suitable fluid such as a clean saline solution. By properly selecting a saline solution of sufficient density, the resulting hydrostatic pressure of the fluid 30 will alone be effective for retaining control of the well until production is commenced.

On the other hand, where the earth formation 15 is to be consolidated by typical sand-consolidating agents, it is generally preferred that the fluid 30 be a so-called "pre-flush fluid" such as kerosene, diesel oil, or a clean saline solution. Once the pressured pre-flush fluid 30 is pumped into the formation 15, one or more consolidating agents (not shown) are successively pumped through the tubing string 11 and into the formation to accomplish the desired consolidation.

As is typical the consolidating fluids may then be followed by a suitable after-flush agent, such as kerosene, as well as in some instances if production is not to be commenced immediately, temporary plugging agentssuch as "Black Magic an oil-base mud as supplied by Oil Base, Inc., of Houston, Texas. It will be recognized that the hydrostatic pressure and the pumping pressure of these successively-injected treating fluids will be greater than the fonnation pressure of the formation 15 so that the perforations 16 will remain open throughout the consolidation operation. The particular nature or type of the sand-consolidation agents employed are, of course, of no significance to the present invention and the consolidating agents may be either porous-setting or solid-setting plastics.

As previously mentioned, the methods of the present invention are also equally applicable for acidizing or hydraulic fracturing operations after the wellhead l7 and the production string 11 are in position. Accordingly, where the formation 15 is to be either acidized or fractured, the fluid 30 will, of course, be the treating fluid or fluids which are typically employed for such operations. Otherwise, the sequence of events will be substantially as depicted in FIGS. 1-4 with the possible exception that the formation 15 may be sufficiently competent that there will be little or no elution of loose formation materials as the debris 26 and 27 is cleared from the perforations 16. In either situation, however, those skilled in the art will appreciate that the new and improved methods of the present invention will be of significant benefit for economically conducting either an acidizing operation or hydraulic fracturing operation.

Turning now to FIG. 5, a preferred embodiment is shown of the new and improved production tool 10 of the present invention. Inasmuch as the preferred tool 10 is especially adapted to utilize a commercially-available tubing plug (such as previously described) for the selectively-releasable barrier means 25 and its detailed arrangement is not within the scope of the present invention, the barrier is only schematically depicted to facilitate the description of the production tool and the valve 24. Thus, in the preferred embodiment of the production tool 10 depicted in FIG. 5 it is preferred that the barrier means 25 be a conventional tubing plug which is adapted to be selectively released from the tool and retrieved to the surface by means of a typical wireline overshot or grapple (not shown).

As illustrated, the production tool 10 includes the new and improved valve 24 and the extended tubular member 21 which is dependently coupled to the valve and has the cap 22 fluidly sealing its lower end. The valve 24 includes an elongated tubular body 31 having threads, as at 32 and 33, respectively arranged at its upper and lower ends for tandemly coupling the valve to the packer 20 and the elongated member 21. In the preferred embodiment of the valve 24, the axial bore 34 of the body 31 is appropriately recessed, as at 35, for receiving the latch fingers or dogs (not shown) of the tubing plug 25 and a selected portion 36 of the axial bore below the recess is particularly sized and located for sealing engagement by the sealing members (not shown) on the tubing plug. Thus, so long as the tubing plug 25 is positioned within the new and improved production tool 10, it will be appreciated that fluid communication is reliably blocked through the axial bore 34.

To provide selective fluid communication between the well bore 12 below the packer 20 and the axial bore 34 when the barrier 25 is positioned therein, one or more lateral ports 37 are provided in the valve body 31 below the initial position of the barrier; and an elongated sleeve 38 is slidably mounted around the valve body and cooperatively arranged for longitudinal movement thereon between a first position blocking fluid communication through the lateral ports and a second position in which the ports are uncovered. In the preferred embodiment of the valve 24, the body 31 includes an enlarged-diameter upper portion 39 defining a downwardly-facing annular space 40. The upper portion of the sleeve 38 is enlarged, as at 41, and complementally fitted in the annular space 40, with inner and outer sealing members 42 and 43 cooperatively arranged thereon for fluidly sealing the enlarged portion of the sleeve in the annular space.

The lower portion of the sleeve 38 is enlarged, as at 44, and a pair of longitudinally-spaced sealing members 45 and 46 are cooperatively arranged therein for sealing engagement with an exterior surface 47 of the body 31 above and below the ports 37 for isolating the ports from the well bore fluids so long as the sleeve is in its illustrated elevated position. To releasably secure the sleeve 38 in its elevated position depicted in FIG. 5, means are provided such as a pin 48 of a predetermined strength for releasably coupling the sleeve to the valve body 31. Accordingly, so long as the valve 24 is in the position depicted in FIG. 5, the barrier 25 will block fluid communication through the axial bore 34 and the ports 37 below the barrier will be isolated from the well bore 12 by the sleeve 38 and the coaction of the sealing members 45 and 46 with the exterior surface 47 of the valve body 31,

It will be appreciated from FIGS. 1 and 5 that when the valve 24 is in its initial position and operatively coupled into the'tool of the present invention, the axial bore 34 below the barrier 25 will be at a reduced pressure (i.e., whatever pressure is initially maintained in the enclosed chamber 23) and the upper portion of the axial bore above the barrier will be in communication with the tubing string 11 above the packer 20. To permit the valve 24 to be selectively opened from the surface, one or more ports 49 are arranged in the valve body 31 to communicate the upper portion of the annular space 40 with the upper portion of the axial bore 34 above the barrier 25. v

Accordingly, to selectively open the valve 24, it is necessary only to increase the fluid pressure in the production string 11 for developing a downwardly-acting pressure force on the enlarged upper end 41 of the sleeve 38 that is sufflcientto fail the pin 48 retaining the sleeve and shift it downwardly in relation to the body 31. Once the sleeve 38 is shifted downwardly to a lower position as determined by an upwardly-facing shoulder 50 around the body 31, the sealing members 45 and 46 will no longer be straddling the ports 37 and one or more lateral ports 51 in the sleeve above the sealing members will be brought into registration with the body ports to establish fluid communication between the well bore 12 below the packer 20 and the enclosed chamber23.

Referring again to FIG. 1, it will be appreciated that when the new and improved tool 10 of the present invention is positioned in the well bore 12, the barrier 25 will be in its initial position and the valve 24 will be in its normally-closed position as depicted in FIG. 5. The' elongated body 21 will define the enclosed chamber 23 so long as the barrier 25 remains in position and'the sleeve 38 remains in its elevated position in relation to the body 31 of the valve 24; a

As previously described in relation to FIG. 3, the valve 24 is selectively opened to induce a rapid flow of connate fluids as at 28 into the enclosed chamber 23 for flushing the debris 26 and 27 from the perforations 16. To accomplish this, the wellhead valve 18 is opened and sufficient pumping pressure is applied from the surface to the fluids in the production string 11 above the packer 20 to fail the shear pin 48 and shift the sleeve 38 downwardly from its position illustrated in FIG. 5 for establishing fluid communication (by way of the ports 37 and 51) between the enclosed chamber 23 and the well bore 12 below the packer. It will, of course, be appreciated that the barrier 25 will still be retained in its depicted position.

As depicted in FIG. 4, once the tubing plug 25 is removed from the production tool 10 by typical wireline retrieval techniques, the fluid 30 can be freely injected through the production string 11 and the now-aligned ports 37 and 51 into the well bore 12 below the packer 20 as required for the particular completion operation. It will, of course, be appreciated that if the cap 22 is left in position on the lower end of the extended tubular member 21, the ports 37 and 51 will tend to limit the flow communication in either direction between the production string 11 and the formation 15. Accordingly, in the preferred embodiment of the production tool 10, the cap 22 is temporarily secured to the tubing member 21, as by a relatively-weak shear pin 52, so that the cap can be easily removed from the extended member either by applying an increased fluid pressure to the production string 11 or by dropping a socalled sinker bar (not shown) into the tubing string once the tubing plug 25 has been removed. By fabricating the cap 22 of either a metal such as aluminum or a rigid plastic material which will ultimately be disintegrated in time by the corrosive action of the well bore fluids,'the debris left in the well bore 12 will be minimized.

Accordingly, it will be appreciated that the present invention has provided new and improved methods and apparatus for completing wells to obtain improved fluid communication between the well bore and selected earth formations traversed thereby without delaying the installation of the production string and the associated wellhead and surface equipment once the drilling operation is concluded. By arranging the new and improved production tool of the present invention in a production string, once the formation interval below the intended position of the production packer has been perforated, the wellhead and other associated surface equipment can be installed in the usual manner without further delay. Then, when the well is to be prepared for production, the valve of the new and improved production tool of the present invention is opened to clear the-perforations of debris and the like. Thereafter, the barrier in the production tool isremoved to establish communication from the surface with the formations below the packer. Where the formations require acidizing, fracturing or consolidation treatments to prepare the well for production, one or more treating fluids can be readily dispatched through the now-opened production string and into the well bore below the packer.

While particular illustrations and embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A method for preparing a well for production of connate fluids from a well bore having a perforated interval with one or more perforations traversing earth formations andcomprising the steps ofzcoupling a normally-closed valve operated by a pressure actuator thereabove between a packer dependently coupled to a string of production piping and a tubular member having a closed lower end for selectively controlling fluid communication between the exterior and interior of said tubular member; releasably positioning a fluid barrier between said valve and said pressure actuator for defining an enclosed chamber in said tubular member and said valve between said fluid barrier and said closed end which is initially at a pressure less than the expected pressure of said connate fluids solong as said valve remains closed and said fluid barrier is in position; lowering said production string into said well bore and setting said packer therein above said perforated interval for isolating said perforated interval from the remainder of said well bore thereabove; coupling'the upper end of said production string to a wellhead for securing said production string in said well bore and providing selective communication from the surface to said pressure actuator by way of said production string above said fluid barrier; varying the pressure in said production string to operate said pressure actuator for opening said valve and drawing said connate fluids into said chamber for expurgating said perforations; and, thereafter, removing said fluid barrier from said production string for establishing communication therethrough between said wellhead and said perforated interval.

2. The method of claim 1 wherein at least the last of the latter two steps is not performed until shortly before production is to be commenced from the well.

3. The method of claim 1 wherein said valve is opened by increasing the pressure in said production string above said fluid barrier.

4. The method of claim 1 wherein said fluid barrier is removed by lowering a grappling device into said production string to secure said grappling device to said fluid barrier; and, thereafter, retrieving said grapplingdevice to bring said fluid barrier to the surface.

5. The method of claim 4 wherein said valve is opened by increasing the pressure in said production string above said fluid barrier.

6. The method of claim 4 wherein said upper pressure-actuated valve is not opened until production is about to be commenced from the well.

7. The method of claim 1 wherein said fluid barrier is positioned before said production string is lowered into said well bore.

min-u.

8. The method of claim 1 further including the step of: opening said closed end of said tubular member after said fluid barrier has been removed to provide increased fluid communication between said wellhead and said perforated interval.

9. Apparatus adapted for producing connate fluids from earth formations traversed by a well bore and comprising: a production string positioned in said well bore between the surface and a perforated interval of said well bore having one or more perforations directed into earth formations adjacent thereto; means adapted for supporting said production string in said well bore and including a wellhead coupled to the upper end of said production string and operatively arranged for selectively controlling communication therewith; a well packer coupled in said production string and operatively arranged for packing-off said well bore to isolate said perforated interval; means adapted for defining an enclosed chamber in said production string including means closing the lower portion of said production string, and a fluid barrier releasably secured therein above said closed lower portion and operatively arranged for selective retrieval to the surface by way of said production string and said wellhead; normally-closed valve means operatively arranged in said production string below said fluid barrier and adapted, upon actuation, for selectively establishing fluid communication between said isolated perforated interval and said enclosed chamber; and pressure actuated means operatively arranged in said production string and adapted for opening said valve means in response to the application of fluid pressure in said production string above said fluid barrier.

10. The apparatus of claim 9 wherein said valve means include a tubular body coupled in said production string and having a fluid passage adapted for providing fluid communication between said isolated perforated interval and said enclosed chamber, and a valve member movably disposed on said tubular body and operatively associated with said valveactuating means for movement thereby from a first position blocking said fluid passage to a second position opening said fluid passage.

11. The apparatus of claim 9 wherein said valve means include a tubular body coupled in said production string and including an internal seat therein adapted for receiving said fluid barrier, first passage means in said tubular body below said internal seat and adapted for providing fluid communication between said isolated perforated interval and said enclosedchamber, and a tubular valve member movably arranged around said tubular body and operatively associated with said valve-actuating means for movement thereby from a first position blocking said first passage means to a second position opening said first passage means,

12. The apparatus of claim 11 wherein said pressure actuated means include a piston chamber arranged on said tubular body, a piston member movably arranged on said tubular body and fluidly sealed within said piston chamber, second passage means in said tubular body and adapted for providing pressure communication between said piston chamber and said production string above said internal seat, and means operable upon movement of said piston member for moving said valve member from its said first position to its said second position.

13. The apparatus of claim 11 wherein said pressure actuated means include an annular piston chamber arranged around said tubular body above and facing said valve member, an annular piston member movably arranged around said tubular body and fluidly sealed within said piston chamber, second passage means in said tubular body and adapted for providing pressure communication between said piston chamber and said production string above said internal seat, and means coupling said valve member and said piston member and adapted, upon downward movement of said piston member, for moving said valve member downwardly from its said first position to its said second position.

14. Apparatus adapted to be used in a well bore having at least one perforated interval traversing earth formations from which connate fluids are to be produced and transported to the surface through a string of production piping having a production packer dependently coupled thereto and supported in the well bore by a wellhead operatively arranged at the surface for selectively controlling communication with the production piping, said apparatus comprising: an elongated body adapted for dependent coupling to a production packer suspended thereabove from a string of production piping and having a longitudinal bore therein adapted to be in communication with such a piping string; means adapted for isolating at least a portion of said longitudinal bore to define a fluid receiving chamber therein and including closure means normally closing the lower portion of said longitudinal bore, and a seat operatively arranged around the upper portion of said longitudinal bore for releasably receiving a fluid barrier adapted for selective retrieval to the surface by way of such a piping string and wellhead; and valve means adapted for selectively controlling fluid communication between a perforated interval isolated by such a production packer and said fluidreceiving chamber when a fluid barrier is positioned in said seat, said valve means including a tubular valve member coaxially mounted around said elongated body and adapted for movement thereon between first and second longitudinallyspaced positions, an annular piston chamber on said elongated body and cooperatively arranged around the upper portion of said valve member, piston means on said upper portion of said valve member within said piston chamber, first passage means normally blocked when said valve member is in its said first position and adapted for providing such fluid communication into said fluid-receiving chamber upon movement of said valve member toward its said second position, and second passage means adapted for providing pressure communication between said piston chamber and said longitudinal bore above said seat for operating said piston means to move said valve member to its said second position for admitting well fluids through said first passage means into said fluid-receiving chamber while a fluid barrier is positioned in said seat.

15. The apparatus of claim 14 further including means releasably securing said closure means to said elongated body and adapted for releasing said closure means therefrom only upon application of force to said closure means after removal of a fluid barrier from said seat.

16. The apparatus of claim 15 wherein said closure means include a plug adapted to be sealingly disposed within said elongated body, said plug being fabricated of a material selected to be corroded by well fluids.

17. The apparatus of claim 14 further including a fluid barrier positioned in said seat, a means cooperatively arranged between said fluid barrier and said elongated body and adapted for releasably securing said fluid barrier in said elongated body.

18. The apparatus of claim 17 wherein said means releasably securing said fluid barrier in said elongated body are adapted for releasing said fluid barrier upon application of force thereto.

19. The apparatus of claim 18 wherein said fluid barrier includes means thereon adapted for coupling said fluid barrier to a cable tool lowered from the surface through a piping string supporting said elongated body.

20. The apparatus of claim 14 further including means releasably retaining said valve member in its said first position on said elongated body and adapted for releasing said valve member for movement toward its said second position only upon an increase of pressure in said piston chamber.

* 4K i l 

1. A method for preparing a well for production of connate fluids from a well bore having a perforated interval with one or more perforations traversing earth formations and comprising the steps of: coupling a normally-closed valve operated by a pressure actuator thereabove between a packer dependently coupled to a string of production piping and a tubular member having a closed lower end for selectively controlling fluid communication between the exterior and interior of said tubular member; releasably positioning a fluid barrier between said valve and said pressure actuator for defining an enclosed chamber in said tubular member and said valve between said fluid barrier and said closed end which is initially at a pressure less than the expected pressure of said connate fluids so long as said valve remains closed and said fluid barrier is in position; lowering said production string into said well bore and setting said packer therein above said perforated interval for isolating said perforated interval from the remainder of said well bore thereabove; coupling the upper end of said production string to a wellhead for securing said production string in said well bore and providing selective communication from the surface to said pressure actuator by way of said production string above said fluid barrier; varying the pressure in said production string to operate said pressure actuator for opening said valve and drawing said connate fluids into said chamber for expurgating said perforations; and, thereafter, removing said fluid barrier from said production string for establishing communication therethrough between said wellhead and said perforated interval.
 2. The method of claim 1 wherein at least the last of the latter two steps is not performed until shortly before production is to be commenced from the well.
 3. The method of claim 1 wherein said valve is opened by increasing the pressure in said production string above said fluid barrier.
 4. The method of claim 1 wherein said fluid barrier is removed by lowering a grappling device into said production string to secure said grappling device to said fluid barrier; and, thereafter, retrieving said grappling device to bring said fluid barrier to the surface.
 5. The method of claim 4 wherein said valve is opened by increasing the pressure in said production string above said fluid barrier.
 6. The method of claim 4 wherein said upper pressure-actuated valve is not opened until production is about to be commenced from the well.
 7. The method of claim 1 wherein said fluid barrier is positioned before said production string is lowered into said well bore.
 8. The method of claim 1 furtHer including the step of: opening said closed end of said tubular member after said fluid barrier has been removed to provide increased fluid communication between said wellhead and said perforated interval.
 9. Apparatus adapted for producing connate fluids from earth formations traversed by a well bore and comprising: a production string positioned in said well bore between the surface and a perforated interval of said well bore having one or more perforations directed into earth formations adjacent thereto; means adapted for supporting said production string in said well bore and including a wellhead coupled to the upper end of said production string and operatively arranged for selectively controlling communication therewith; a well packer coupled in said production string and operatively arranged for packing-off said well bore to isolate said perforated interval; means adapted for defining an enclosed chamber in said production string including means closing the lower portion of said production string, and a fluid barrier releasably secured therein above said closed lower portion and operatively arranged for selective retrieval to the surface by way of said production string and said wellhead; normally-closed valve means operatively arranged in said production string below said fluid barrier and adapted, upon actuation, for selectively establishing fluid communication between said isolated perforated interval and said enclosed chamber; and pressure actuated means operatively arranged in said production string and adapted for opening said valve means in response to the application of fluid pressure in said production string above said fluid barrier.
 10. The apparatus of claim 9 wherein said valve means include a tubular body coupled in said production string and having a fluid passage adapted for providing fluid communication between said isolated perforated interval and said enclosed chamber, and a valve member movably disposed on said tubular body and operatively associated with said valve-actuating means for movement thereby from a first position blocking said fluid passage to a second position opening said fluid passage.
 11. The apparatus of claim 9 wherein said valve means include a tubular body coupled in said production string and including an internal seat therein adapted for receiving said fluid barrier, first passage means in said tubular body below said internal seat and adapted for providing fluid communication between said isolated perforated interval and said enclosed chamber, and a tubular valve member movably arranged around said tubular body and operatively associated with said valve-actuating means for movement thereby from a first position blocking said first passage means to a second position opening said first passage means.
 12. The apparatus of claim 11 wherein said pressure actuated means include a piston chamber arranged on said tubular body, a piston member movably arranged on said tubular body and fluidly sealed within said piston chamber, second passage means in said tubular body and adapted for providing pressure communication between said piston chamber and said production string above said internal seat, and means operable upon movement of said piston member for moving said valve member from its said first position to its said second position.
 13. The apparatus of claim 11 wherein said pressure actuated means include an annular piston chamber arranged around said tubular body above and facing said valve member, an annular piston member movably arranged around said tubular body and fluidly sealed within said piston chamber, second passage means in said tubular body and adapted for providing pressure communication between said piston chamber and said production string above said internal seat, and means coupling said valve member and said piston member and adapted, upon downward movement of said piston member, for moving said valve member downwardly from its said first position to its said second position.
 14. APparatus adapted to be used in a well bore having at least one perforated interval traversing earth formations from which connate fluids are to be produced and transported to the surface through a string of production piping having a production packer dependently coupled thereto and supported in the well bore by a wellhead operatively arranged at the surface for selectively controlling communication with the production piping, said apparatus comprising: an elongated body adapted for dependent coupling to a production packer suspended thereabove from a string of production piping and having a longitudinal bore therein adapted to be in communication with such a piping string; means adapted for isolating at least a portion of said longitudinal bore to define a fluid-receiving chamber therein and including closure means normally closing the lower portion of said longitudinal bore, and a seat operatively arranged around the upper portion of said longitudinal bore for releasably receiving a fluid barrier adapted for selective retrieval to the surface by way of such a piping string and wellhead; and valve means adapted for selectively controlling fluid communication between a perforated interval isolated by such a production packer and said fluid-receiving chamber when a fluid barrier is positioned in said seat, said valve means including a tubular valve member coaxially mounted around said elongated body and adapted for movement thereon between first and second longitudinally-spaced positions, an annular piston chamber on said elongated body and cooperatively arranged around the upper portion of said valve member, piston means on said upper portion of said valve member within said piston chamber, first passage means normally blocked when said valve member is in its said first position and adapted for providing such fluid communication into said fluid-receiving chamber upon movement of said valve member toward its said second position, and second passage means adapted for providing pressure communication between said piston chamber and said longitudinal bore above said seat for operating said piston means to move said valve member to its said second position for admitting well fluids through said first passage means into said fluid-receiving chamber while a fluid barrier is positioned in said seat.
 15. The apparatus of claim 14 further including means releasably securing said closure means to said elongated body and adapted for releasing said closure means therefrom only upon application of force to said closure means after removal of a fluid barrier from said seat.
 16. The apparatus of claim 15 wherein said closure means include a plug adapted to be sealingly disposed within said elongated body, said plug being fabricated of a material selected to be corroded by well fluids.
 17. The apparatus of claim 14 further including a fluid barrier positioned in said seat, a means cooperatively arranged between said fluid barrier and said elongated body and adapted for releasably securing said fluid barrier in said elongated body.
 18. The apparatus of claim 17 wherein said means releasably securing said fluid barrier in said elongated body are adapted for releasing said fluid barrier upon application of force thereto.
 19. The apparatus of claim 18 wherein said fluid barrier includes means thereon adapted for coupling said fluid barrier to a cable tool lowered from the surface through a piping string supporting said elongated body.
 20. The apparatus of claim 14 further including means releasably retaining said valve member in its said first position on said elongated body and adapted for releasing said valve member for movement toward its said second position only upon an increase of pressure in said piston chamber. 